1. Field of the Invention
The present invention relates to a torch cable disposition structure for an industrial robot including an arc-welding torch.
2. Description of the Related Art
As one representative application of a robot, there is an arc-welding robot. The arc-welding robot is an industrial robot that executes arc-welding on a work using an arc-welding torch (hereinafter simply referred to as a “welding torch”) mounted on a part of the robot near the front end of an arm. In a shop floor where the arc-welding robot is used, welding work must be carried out, in many cases, by putting an arm of the arc-welding robot into a narrow space between the work pieces, tools, and peripheral equipment. In these cases, interference can easily occur on the basis of the moving of the arc-welding robot.
Particularly, the torch cable that is connected to the welding torch has a risk of interference with the surrounding work pieces, tools, and peripheral equipment, as compared with the arm and the welding torch, at the front end of the robot, that move in a relatively narrow area. One of reasons for this is that the torch cable is loosely laid around a robot main body to secure stability of feeding a welding wire, and this increases the area of the interference with the surrounding.
In this situation, some proposals have been made to solve the interference of the torch cable. FIG. 1 is a front view of an arc-welding robot system that employs the torch cable disposition structure disclosed in Japanese Patent Application No. 2003-14942 (Japanese Unexamined Patent Publication No. 2004-223576). As shown in FIG. 1, a first wrist element 11 is rotatably provided around a first axis line A, on the front end of a forearm base 10 of an arc-welding robot (hereinafter also simply referred to as a “robot”). A second wrist element 12 is rotatably or pivotably provided around a second axis line B, on the first wrist element 11. A welding torch 2 is rotatably or pivotably supported around a third axis line C via a transmission mechanism 13. The third axis line C is disposed approximately perpendicular to the second axis line B and is separated from the first axis line A by a predetermined distance. In other words, the welding torch 2 is rotatably or pivotably supported around the axis C parallel with a final rotation axis of the robot offset by a certain amount.
A sliding mechanism 6 is provided on the forearm base 10 via a supporting base 5, and a wire feeder 4 is mounted on the sliding mechanism 6. The wire feeder 4 draws a welding wire from a welding wire drum, and feeds the welding wire to the welding torch 2 using a torch cable 3. A welding power supply unit 21 supplies power to the welding wire and the wire feeder via a power feeder 22. A power supply control (i.e., a control of a welding voltage and a welding current, and a control of a wire feeding) is carried out based on an instruction transmitted from a robot controller 20 to the welding power supply unit 21.
The sliding mechanism 6 on the forearm base 10 is reciprocally movable along a direction approximately parallel with the first axis line A. The wire feeder 4 is mounted on the sliding mechanism 6. The sliding mechanism 6 utilizes a linear motor controlled by the robot controller 20. Therefore, the robot controller 20 can also control the position of the wire feeder 4 on the sliding mechanism 6 to suitably maintain the tension of the torch cable 3.
As described above, in the torch cable disposition structure disclosed in Japanese Patent Application No. 2003-14942, the welding torch 2 is rotatably provided around the axis parallel with a final rotation axis of the robot but offset by a certain amount. At the same time, the wire feeder 4 is slidably mounted on the forearm base 10 of the robot. Therefore, even when the posture of the welding torch 2 is changed, the posture of the torch cable 3 hardly changes. As a result, the interference between the torch cable 3 and the workpiece, the tool, and the peripheral equipment can be minimized, thereby realizing a stable feeding of the welding wire.
There is also proposed a method of pulling a slider for slidably mounting the wire feeder onto the forearm base of the robot, to rearward of the forearm, thereby preventing the torch cable from being excessively pulled or excessively loosened, as disclosed in Japanese Patent Application No. 2004-71304.
However, even when the measures disclosed in Japanese Patent Application No. 2003-14942 and Japanese Patent Application No. 2004-71304 are taken, a margin is necessary, in the space above the welding robot and the space behind the robot, because the wire feeder is mounted on the sliding mechanism provided on the forearm base. In other words, as can be easily understood from FIG. 1, the wire feeder is positioned above the sliding mechanism provided on the forearm base. Further, the wire feeder moves toward obliquely above and behind the forearm on the sliding mechanism, and also pivots around the D axis together with the forearm. Therefore, when sufficient space is not present around the forearm, the wire feeder has a risk of interference with external devices and wall surfaces.
It is an object of the present invention to provide a torch cable disposition structure for an arc-welding robot that can avoid interference due to the mounting of a wire feeder on the forearm, while taking advantage of the prevention of an excessive loosening or tension of the torch cable obtained by the sliding mechanism.